If this was Stormbringer/Elric! we were talking about I'd fully agree with you, but in Magic World all we're left with from the old games is the mechanics and not a lot of guidance on what something "is." As a generic fantasy RPG it seems like this was done intentionally to leave it up to the GM to define.

In Magic World terms I tend to think of demons as being something like jinn; amorphous entities of some otherworldly plane/dimension/reality that lack individuality until they are drawn forth and formed in the material world. Mechanically this explains sorcerer's being able to define a demon. in Cosmological terms, maybe this is one reason why they are so eager to make deals with sorcerers or allow themselves to be summoned at all? They become "real" (or at least more real) once they are summoned.
Whatever demons are and where they come from, I tend to want to rebel against the carefully laid out cosmology by Gary Gygax for the Dungeons & Dragons game with its outer planes and their clearly defined hierarchies, species, politics, etc.

The rights were lost ages ago, and I don't know really know how amenable Michael Moorcock is to licensing his IPs to Chaosium (or anybody) these days. My guess is that there's not a lot of profit to be made even if they did re-acquire the rights.
"Who knows?," is the only answer most people are going to be able to come up with is my guess.

I'm saddened for Greg's family and his close friends and they have my deep sympathies, but what a legacy to leave behind. One of the true creative geniuses, and by all accounts just an excellent human being.

This thread has me thinking about how the game would look if the only spells available were summon elemental, summon demon, and summon spirit? I'm kind of thinking it would function the same way as the sandestins in Jack Vance's Dying Earth or Lyonesse novels.
I think I've got one player who might balk - he loves his Deep Magic users, but I can envision some interesting dynamics in play.

I can definitely see an argument for removing the POW cost or at least include it as an option in the interest of allowing the "dread necromancer" trope who raises scores of undead to harrass his enemies. Maybe there's a middle ground? Allow the POW investment for more permanent undead and without the POW investment, any created undead only persist for POW hours, or they decay at the rate of 1 HP per hour or something? I need to look at the necromancy rules again and refresh my memory about the possibilities, but I think there's a lot of minor tweaks that could be made to enhance the proposition of being a dedicated corporeal necromancer.

I guess if you take only the narrowest interpretation of the rules, then it's not explicit, but attacking a "defenseless" opponent is an "easy" roll in the RAW. How the victim of an attack gets to "defenseless;" either because they've run out of parries/dodges, or just choose not to parry/dodge (for some crazy reason) doesn't seem all that difficult to draw a line between the two concepts. As for your D&D character example. needing to get a 10+ on a D20 roll is 55%. Sure some characters will have bonuses from Strength, etc.but it's not an average of 75%.
Anyway, no system is perfect at modeling physics/reality. If you don't like something then make your own rules -- In this example you could easily state that the only way to fail an attack roll vs. a defenseless opponent is to fumble. A house-rule like that won't break the game, I promise.

Maybe read the section on backstabs and helpless opponents (pg 215 of the BGB). A character who chooses not to parry or dodge is basically identical to a character who can't parry or dodge, so all attacks against them would be "easy." So in your example above, the chance to hit rises to 60%.
As to how I would conceptualize the idea of not automatically succeeding? Well, maybe the attacker winds up and swings and doesn't actually hit with the sweet spot of the weapon? Hell, there's plenty of times I've been choppiing some perfectly defenseless firewood with a splitting maul, and hit at a slightly odd angle which deflected the blade into the chopping block and didn't cut the piece of wood at all. So while I might have "hit" a glancing blow against the piece of wood, I didn't "succeed" and no real damage was suffered by it. Why should it be any different if you were trying to whack somebody with a stick, a bat, a sword? Even without somebody actively avoiding a blow, you could accidentally slap somebody with the flat of a blade, or hit with the haft, or do something else that connects, but doesn't inflict real damage.
I think the key point is that achieving contact is not the same as achieving a "success."

I have no idea what you are replying to me for? @tooley1chris said he wasn't sure where he wanted to put his energy: BGB or MW. I said I didn't think it would matter to Chaosium's sales one way or another (and then explained Chaosium's current strategy, which doesn't criticize or question their strategy).

The BGB ain't exactly a priority for Chaosium either. But since the two games are so broadly compatible, I doubt there's any harm in putting your efforts into one vs another. For what it's worth, Chaosium seem to be pretty zeroed-in on RQG and CoC (which makes financial sense) and there's a couple of other things in the pipeline that seem to be moving away from generic systems towards games with tightly integrated settings and rules. Fan-support of MW or the BGB isn't going to hurt (or help) their bottom line, it's all about finding players who want to play in your games, and running whatever system clicks for you, whether it's old or new, supported or not.

I still play Magic World (and I worked like hell on my form-fillable character sheet, and an NPC generator that I just uploaded a month or so ago here in the downloads section if you want to give them a look).
Personally, I'm just about to start a new campaign adapting Gavin Norman's Dolmenwood setting to MW and I'm excited for it to begin in a few weeks. As for Classic Fantasy, it did indeed get released by The Design Mechanism, and it's pretty good from what I've read, plus they released several adventures for it. RuneQuest: Glorantha is in the process of being rolled out and the main rule-book and the bestiary are available; it's tailor-made to run games in Glorantha and doesn't seem like it's suited for any kind of homebrew game settings, but there's some interesting ideas in it.
With respect to modules, adventures, settings, I think they'd be appreciated by the people that still play Magic World, and it's always easy enough to convert stuff from one D100 system to another. Follow your bliss I say.